1. Field of the Invention
This invention relates broadly to medical devices incorporating elements having a low modulus of elasticity. More particularly, this invention relates to medical devices incorporating one or more cable elements made from a plurality of twisted and drawn wires, at least one of the wires comprising a nickel-titanium alloy.
2. State of the Art
Wires are utilized throughout the medical arts. In many medical devices a particularly desirable feature for the wires is high elasticity. For example, in baskets and snares high elasticity may be the most important property of the wires used. The elasticity of the wires comprising snares and baskets is a factor in the extent to which each may be compressed for insertion to the surgical site and yet still be able to expand upon use. In addition, higher elasticity permits the baskets and snares to be contracted about smaller radii.
The need for highly flexible self-expanding stents is also well-known. Flexibility not only permits proper stent deployment, but also enables the stent to better conform to the vascular walls.
In endoscopic instruments, a control wire is often coupled between a proximal handle and a distal end effector. The control wire is used to translate movement of the handle into operation of the end effector. The wire must be able to easily bend through the tortuous paths through which endoscopic instruments are guided.
Wire flexibility is also important in numerous other medical devices. For that reason, the medical arts have recently had much interest in nickel-titanium alloy (Nitinol) wires which exhibit superelastic characteristics. For the same reasons which have made Nitinol so popular, an even more elastic wire than a nickel-titanium wire is desirable for many medical device applications.
In addition, with respect to many medical devices, the art has gone to great lengths and expense to provide radiopaque materials to the distal end of Nitinol elements (see, e.g., U.S. Pat. No. 5,520,194 to Miyata et al.). This is particularly required in devices using very fine (i.e., small diameter) Nitinol wires which cannot easily be seen during fluoroscopy. However, radiopaque materials are difficult to attach to the Nitinol components owing, in part, to their dissimilarity with the Nitinol material. Moreover, it is preferable in certain applications to have a highly elastic component which conducts electricity sufficiently to permit cautery functions or to permit the component to function as an electrical lead. However, nickel-titanium alloys are not particularly good conductors.